1. Field of the Invention
The invention is in the field of pollution control, particularly in the remediation and cleaning of incomplete combustion products of carbon-containing fuels. More particularly, the present invention is in the field of the degradation and cleaning of incomplete combustion products like soot, hydrocarbons, carbon monoxide and other pollutants produced by internal combustion engines, such as diesel engines, and industrial burners, such as those that burn coal, fuel oil or other carbon-containing fuels.
2. Review of the Relevant Technologies
Modem society has mastered the art of producing new goods but struggles to dispose of its wastes. One problem associated with the modem economy involves pollutants that are produced by burning carbon-containing fuels, mainly fossil fuels, such as by internal combustion engines and industrial burners. The incomplete combustion of carbon-containing fuels such as gasoline, diesel fuel, fuel oil, coal, wood, biomass and even natural gas can result in the generation of pollutants such as carbon particulates, hydrocarbons, soot, oily substances, carbon monoxide (CO) and other pollutants. Such pollutants collect in the atmosphere and can cause all manner of health problems and smog. In response to the buildup of atmospheric pollution governments have attempted to legislate strict controls on the output of pollution generated by carbon-containing fuels.
For example, in response to pollution caused by gasoline-powered internal combustion engines, catalytic converters have been developed and mandated to reduce the levels of incomplete combustion pollutants emitted into the environment by gasolinepowered vehicles. Catalytic converters are typically positioned in-line with the exhaust and muffling system of an internal combustion engine and are generally able to catalytically convert most of the unburnt hydrocarbons and CO into CO2 and water. Conventional catalytic converters contain palladium or platinum, which are coated on top of carrier beads or pellets made of inert and heat-resistant materials such as ceramics in order to increase the surface area of the active catalyst and keep them from simply blowing out the exhaust pipe. Surface coating a less expensive substrate with the catalytic metal also decreases the cost of the catalyst particles since most catalytic metals tend to be quite expensive. Because leadbased additives (i.e., tetraethyl lead) added to some gasolines can xe2x80x9cpoisonxe2x80x9d or destroy the usefulness of the catalyst, such additives have been effectively banned in the United States.
Although modern catalytic converters can be used to convert unburnt hydrocarbons and CO into carbon dioxide (CO2) and water, they are generally only feasible for use with relatively clean burning systems such as gasoline-powered vehicles. They generally are not suitable for use with diesel engines. Because of the nature of diesel engines, both in terms of the fuel that is burned, as well as the way in which the fuel is burned, diesel engines produce substantial quantities of soot and other unburnt hydrocarbons which are too plentiful to be efficiently converted into CO2 and water using reasonably sized and priced catalytic converters. Although they are known to generate substantial quantities of air-borne pollution, diesel engines have been largely exempted from the stringent air quality guidelines presently applied to gasoline-powered vehicles for largely economic reasons. Diesel engines are used for most long-haul shipping such as by tractor-trailers and trains and their elimination might cause dire economic problems. Nevertheless, researchers have struggled for years to find an effective and economical way to remove pollutants from the exhaust stream of diesel engines.
More recently, however, public concern has translated into increased political pressure to strengthen emission standards for diesel engines. There is a possibility that emission guidelines will be imposed in certain states that may be difficult, if not impossible, to meet in an economically feasible manner using conventional catalytic converters. The tendency of diesel engines to produce soot and other unburnt hydrocarbons at a rate that is many times that produced by gasoline-powered engines would require the use of far greater amounts of expensive catalyst using existing technology. However, one of the reasons why diesel engines have been exempted from air pollution standards in the first play is the tremendous cost that would be incurred in mandating the use of conventional catalytic converters to remediate the pollution caused by diesel engines.
Researchers have also struggled to find ways to effectively and economically address the tremendous quantity of pollutants generated by industrial burners, such as those that burn coal, fuel oil, or natural gas. In response to pollution controls directed to industrial burners, sophisticated scrubbers and after burners have been developed in attempts to satisfy such pollution standards. However, these and other pollution reduction means can be quite expensive, both in retrofitting older industrial burners as well as in the fabrication of new ones.
Finally, even assuming one could construct a perfectly effective catalytic converter for carbonaceous particulates, hydrocarbons and CO, the end result would still be the generation of equal or greater amounts of CO2 compared to what is presently being generated. Although inert and non-polluting, CO2 is still of concern to environmentalists due to the fear that the buildup of excessive amounts of CO2 in the atmosphere has resulted in detectable global warming, although a minority of scientists remain skeptical, and will eventually result in catastrophic climatic changes if the world continues to generate CO2 in high quantities. Since there does not appear to be any end in sight of the need to burn fossil fuels, the concentration of CO2 will invariably continue to increase indefinitely.
In view of the foregoing, it would be an advancement in the art to provide methods and systems that could effectively and inexpensively eliminate, or at least substantially reduce, the quantity of unburnt or partially burnt combustion products produced by diesel engines and other internal combustion engines in an economically feasible manner.
It would be a further advancement in the art to provide methods and systems for eliminating, or at least greatly reducing, the quantity of incomplete combustion products produced by diesel engines, industrial burners, and other systems that bum fossil fuels which would eliminate the need for expensive catalysts, such as palladium, platinum and other rare and expensive metals.
It would yet be an advancement in the art if such methods and systems could be easily adapted, such as by upscaling or downscaling, in order to catalytically degrade waste combustion products produced by virtually any system that burned carbon-containing fuels, such as diesel trucks, trains, other vehicles, power plants, metal smelters, and virtually any industrial burner.
It would be an additional advancement if such methods and systems were able to reduce the quantity of CO2 that is emitted into the atmosphere as a result of the burning of fossil fuels or other carbon-containing fuels.
Such methods and systems for catalytically destroying unburnt carbon particulates, soot, waste hydrocarbons, oily substances, CO and other pollutants produced by the incomplete combustion of carbon-containing fuels are disclosed and claimed herein.
The present invention relates to methods and systems for degrading and cleaning incomplete combustion products produced during the combustion of carbon-containing fuels. More particularly, the invention encompasses methods and systems that utilize a highly reactive environment generated by the complex interaction of a heated waste gas stream of incomplete combustion products, moisture, carbon dioxide, oxygen, and possibly other gaseous or fine particulate materials, with a bed of silica- or alumina-based catalytic media.
The highly reactive environment so generated has been found to be amazingly effective in eliminating at least a portion of carbon particulates, soot, hydrocarbons, CO, oily substances, and other unburnt organic materials produced during incomplete combustion of carbon-containing fuels. The inventive methods and systems are especially useful for the degradation of incomplete combustion products produced by diesel and other internal combustion engines and industrial burners, such as coal or fuel oil fired power plants, metal smelters and the like. Rather than using expensive catalysts such as those presently used to catalyze the conversion of soot, hydrocarbons and CO to CO2 and water, the present invention utilizes particles such as silica which, under certain conditions, have been found to generate a highly reactive environment in the vicinity of the silica particles that is able to at least partially destroy many different kinds of incomplete combustion products. Silica particles, while conventionally believed to be entirely inert, are now believed to be capable of generating a localized region of highly reactive hydroxyl radicals and other highly reactive molecular fragments on their surface and within the vicinity of such particles under certain conditions to be discussed herein.
Although the technology of providing a fluidized bed of inert silica and alumina to assist in the pyrolysis or cracking of certain organic materials is well-known, it was heretofore unknown that such particles could also generate hydroxyl radicals under certain conditions. Instead, such particles were used mainly to better distribute heat throughout the fluidized bed and provide a scouring action in some cases. An example of a fluidized bed is found in European Patent Application Publication No. 0,176,123, filed Aug. 26, 1985, in the name of Geeroms (hereinafter xe2x80x9cEU ""123xe2x80x9d), which discloses a xe2x80x9cwhirl bedxe2x80x9d comprising a metal chamber, inert fluidizable particles such as silica, means for introducing heated gases through the fluidizable particles, and an afterburner for burning any gases that are formed by pyrolysis. The purpose for the whirl bed in EU ""123 is to clean metal parts upon which paint, rubber, or other hard-to-remove substances have adhered. EU ""123 appears to rely, however, on the combination of the abrasive action of the whirling sand media and a high temperatures (preferably 650xc2x0 C. or above) to effect the pyrolytic and mechanical removal of the adhered organic substances to clean the metal parts.
While it is true that at temperatures high enough to effect pyrolysis silica and alumina appear to be entirely inert, it has heretofore not been understood that silica (and possibly alumina) are able, at temperatures ranging from as low as perhaps 30xc2x0 C. up to perhaps 500xc2x0 C., and in the presence of moisture, are apparently able to generate a localized, yet highly reactive, region or atmosphere containing highly reactive hydroxyl radicals and, perhaps, other highly reactive molecular fragments or moieties, that are able to at least partially degrade organic materials, including the incomplete combustion products of carbon-containing fuels. In particular, the inventors of the present technology have discovered that an abundance of very reactive hydroxyl radicals and other reactive hydrogen oxide species (and possibly other oxide or oxidizing species) can apparently be generated by silica and alumina under certain conditions and which are capable of destroying soot, unburnt hydrocarbons, CO and other incomplete combustion products at temperatures far below their respective combustion temperatures. Such pollutants are not being destroyed by combustion but by the highly reactive hydroxyl radicals and other reactive species believed to be generated by the interaction between moisture and silica or alumina particles in a surface phenomenon.
In a preferred embodiment, the silica and/or alumina particles are suspended or fluidized in a fairly static condition against the force of gravity by means of air flowing upwards through the particles. Such airflow can be provided by any gas pressurizing means known in the art, including turbines, fans, pumps, the inherent pressure generated by internal combustion engines, and combinations of the foregoing. Suspending or fluidizing the particles greatly increases the active surface area of the silica and/or alumina particles by separating them slightly and allowing for more gas-to-particle contact.
As stated above, it now appears that hydroxyl radicals can be generated at relatively low temperatures, perhaps as low as about 30xc2x0 C., up to about 500xc2x0 C. The reaction chamber is preferably heated and maintained at temperatures in a range of about 50xc2x0 C. to about 400xc2x0 C., more preferably in a range of about 75xc2x0 C. to about 350xc2x0 C., and most preferably in a range of about 100xc2x0 C. to about 300xc2x0 C. Such temperatures are preferred in view of their being generally within the temperature range of exhaust gases generated by internal combustion engines after passing through the exhaust system. Although such temperatures are preferred, the degradation of soot, hydrocarbons, CO and other incomplete combustion products of carbon-containing fuels by means of hydroxyl radicals and other reactive species generated by silica, alumina and the like at any temperature would be within the scope of the invention.
The heat necessary to maintain the reaction chamber within the desired temperature range can be provided by any source. In a preferred embodiment, the heat will be provided substantially, or even exclusively, by the exhaust gases themselves. Nevertheless, it is certainly within the scope of the invention to supplement the heat found in exhaust gases by means of electric heaters, burning fuels such as methane gas, by recycling heat recovered from other sources, or by any other heat source that is able to provide a desired quantity of heat in order to maintain the reaction chamber within a desired temperature range. For example, at initial startup of a diesel engine, or after extensive idling or downhill travel, the exhaust gases generated by the diesel engine may be too cold to adequately heat the reaction chamber. In such cases it may be desirable to provide supplemental heating in order to raise and then maintain the temperature in order to ensure efficient degradation of soot, hydrocarbons and other incomplete combustion products.
Providing an oxygen-rich environment would be expected to increase the oxidative breakdown of the organic wastes, although breakdown has been observed in an oxygen-poor environment within the reaction chamber so long as the media particles have been exposed to some degree of moisture. The apparatus may optionally include means for introducing a variety of gases within the reaction chamber, such water vapor, oxygen, ammonia, etc. One such means for introducing gases is the diffusion pipe or pipes used to introduce the incomplete combustion products into the reaction chamber. Another might be a separate port feeding into the reaction chamber.
In a preferred embodiment, the means for suspending the media, maintaining the temperature at the desired level, introducing exhaust gases to be treated, and optionally introducing oxygen and water vapor rich gas into the reaction chamber comprise one or more diffusion pipes containing spaced-apart diffusion holes submerged beneath a bed of silica or alumina. In many cases it will not be necessary to enrich the reaction chamber with water vapor since exhaust gases typically contain abundant water vapor as a result of the combustion of the hydrogen portion of hydrocarbon fuels. Sensors can be placed within the reaction chamber in order to regulate the inputs of water vapor, oxygen, heat, etc.
Because of the extremely simple apparatus used to carry out the reaction process, it is possible to greatly upscale or downscale the reaction apparatus size to accommodate a wide variety of uses and applications. The reaction chambers may be very large or utilized in series in order to serve large industrial needs such as coal or petroleum fired power plants, smelters and the like. Alternatively, they may be downsized and adapted for use in catalytically treating exhaust gases produced by internal combustion engines, e.g. diesel-, gasoline-, and propane-powered engines.
Exhaust gases from the burning of carbon-containing fuels typically comprises incomplete combustion products, which may include carbon soot, gaseous, liquid or particulate hydrocarbons, carbon monoxide, and diatomic hydrogen, among other compounds. Actual laboratory testing has shown that passing exhaust gases produced by a diesel engine through a reaction chamber containing fluidized silica particles greatly reduces both the level of soot produced by the combustion of diesel fuel as well as carbon monoxide.
Although such pollutants would be expected be converted into CO2 or a mixture of CO2 and water, one of the startling discoveries has been a dramatic decrease in the concentration of CO2 in the exhaust stream after being passed through the reaction chamber, as well as a dramatic increase in the oxygen content. Although not entirely understand, it may be that the carbon monoxide and/or carbon dioxide may actually react with silica to yield silicon carbide, together with the concomitant release of oxygen. In addition, nitrogen oxides (NOx) have apparently been reduced by about 90%, presumably to nitrogen gas, or possibly even to silicon nitride in a modified, catalyzed carbothermal reaction that may involve one or more of particulate carbon, hydrocarbons, CO or CO2. The inventors have not ruled out other possible reaction sequences that seem to be consuming the CO2. Finally, it is believed that the methods and systems are able to at least partially eliminate sulfer dioxide.
In view of the foregoing, it is an object to provide methods and systems that effectively and inexpensively eliminate, or at least substantially reduce, the quantity of unburnt or partially burnt combustion products produced by diesel engines and other internal combustion engines in an economically feasible manner.
It is a further object to provide methods and systems for eliminating, or at least greatly reducing, the quantity of incomplete combustion products produced by diesel engines, industrial burners, and other systems that burn fossil fuels, thereby eliminating the need for expensive catalysts, such as palladium, platinum and other rare and expensive metals.
It is yet an object to provide methods and systems that can be easily adapted, such as by upscaling or downscaling, in order to catalytically degrade waste combustion products produced by virtually any system that burned carbon-containing fuels, such as diesel trucks, trains, other vehicles, power plants, metal smelters, and virtually any industrial burner.
It is an additional object and feature to provide methods and systems that are able to reduce the quantity of CO2 that is emitted into the atmosphere as a result of the burning of fossil fuels or other carbon-containing fuels.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.